1. Field of the Invention
This invention relates generally to the commercial refrigeration art, and more particularly to improvements in food product merchandisers and defrost control systems therefor.
2. Related Application
This application discloses improvement subject matter in common with co-pending and commonly-owned application Ser. No. 08/655,157 filed May 29, 1996 (as a continuation of Ser. No. 08/407,676 filed Mar. 14, 1995) and entitled Refrigerated Merchandiser With Modular Evaporator Coils and EEPR Control, now U.S. Pat. No. 5,743,098.
3. Description of Prior Art
Great advances have been made in the last forty years in the field of commercial food merchandising with the improved insulation materials, better refrigerants, more efficient air handlers and condensing unit systems, better lighting and the universal use of ambient air temperature and humidity control in food stores and the like. A long checklist of important factors influence the construction and manufacture of food merchandisers including refrigeration requirements and performance, structural engineering for strength, durability and safety as well as insulation effect, servicing capability, product merchandising potential, and both manufacturing and operating costs.
In today's marketplace a wide variety of food merchandisers are used to best market different types of food products as well as meet their cooling needs. In the low temperature field, frozen food merchandisers maintain product display temperatures at about 0.degree. F. and ice cream cases operate at about -5.degree. F. to -10.degree. F. Frozen foods are best protected in reach-in coolers (with glass front doors), but open front, multi-deck merchandisers best display various food products. Similarly, in the medium temperature field of 28.degree. F. to 50.degree. F. product temperatures, glass front deli merchandisers are generally preferred for the marketing of freshly cut meats, cheeses, salads and other deli items, but open front multideck merchandisers are widely used for packaged meat and dairy products and single deck cases are preferred for fresh produce.
Although there has been some industry standardization at eight (8') foot and twelve (12') foot merchandiser lengths, the manufacture of commercial refrigerator fixtures has generally remained a hands-on operation. Thus, in the past, most commercial merchandisers have been cooled by conventional vapor phase refrigerant systems and typically have utilized fin and tube type evaporator coils which extend the full length of the merchandiser to best achieve uniform air cooling for delivery to the product area from end-to-end throughout the length of the merchandiser. In some of these applications, the evaporator coil was divided or split into two or more full length sections connected in series refrigerant flow relationship and typically arranged in a sequential air flow relationship in the bottom section and/or immediately adjacent in the lower back wall of the merchandiser cabinet. More recently, there has been development work in utilizing non-compressible liquid chemical coolants (so called "glycol-type" systems using glycol or ethylene solutions or some other secondary heat transfer liquid) for producing the merchandiser cooling effect; but conventional types of cooling coil configurations have been employed for these systems. In any event, such coils and the control valving therefor were generally accessible only from the inner lower well area of the product zone for maintenance or service. Such a location does not interfere with the structural soundness of a coffin-type merchandiser, but full length back wall coil locations limit the structural support capability for internal vertical frames in multi-deck merchandisers, as well as the cantilever suspension of glass front panels in deli merchandisers, as in commonly assigned U.S. Pat. No. 5,639,149.
The commonly assigned, co-pending application Ser. No. 08/655,157 (U.S. Pat. No. 5,743,098) discloses improvements in an air cooling and control system for a refrigerated food merchandiser having plural modular cooling coil sections of preselected heat exchange potential and being arranged in horizontally spaced apart disposition, and refrigerant metering means for controlling liquid refrigerant flow on the high (inlet) side of the evaporator sections, and other refrigerant metering and electronic control means for regulating suction pressure and refrigerant vapor flow on the low (outlet) side of the evaporator sections.
Another commonly owned U.S. Pat. No. 5,577,826 disclosed modular external frame structures for refrigerated merchandisers whereby to better accommodate placement of the modular coil section arrangements of U.S. Pat. No. 5,743,098